I don't trust software developers to provide much backwards comparability, so you could spend months rating all your photos and then in 2015 be forced to rate them all again on your new software.
Therefore:
I organize my photos in folders. This way I don't risk losing my categories if I change software and it can be transferred to another machine or DVD very easily and will browse logically with categories preserved even on a DVD player or TV, for example.
For example I will have a folder structure something like this:
"My Photos" > "2011" > "Birds" or
"My Photos" > "2011" > "Portraits"
I also use
NameEXIF to name my files by date and time automatically.
That's it. If you need more specific categories, you can just add more folders. So have Birds subfolders: Parrots, Pigeons or whatever. If you want rate a file, then you can just browse the folders in a program like Picassa and apply a star, or make specific folders for "5 star Parrots" "4 Star Parrots". The number of folders you need should be balanced between being too specific and not specific enough. I get by with about 10 categories for about 2000-3000 photos per year.